[PATCH net-next] net/smc: cap allocation order for SMC-R physically contiguous buffers

["D. Wythe" <alibuda@linux.alibaba.com>]

The alloc_page() cannot satisfy requests exceeding MAX_PAGE_ORDER,
and attempting such allocations will lead to guaranteed failures
and potential kernel warnings.

For SMCR_PHYS_CONT_BUFS, cap the allocation order to MAX_PAGE_ORDER.
This ensures the attempts to allocate the largest possible physically
contiguous chunk succeed, instead of failing with an invalid order.
This also avoids redundant "try-fail-degrade" cycles in
__smc_buf_create().

For SMCR_MIXED_BUFS, if its order exceeds MAX_PAGE_ORDER, skip the
doomed physical allocation attempt and fallback to virtual memory
immediately.

Signed-off-by: D. Wythe <alibuda@linux.alibaba.com>
Reviewed-by: Dust Li <dust.li@linux.alibaba.com>
---
 net/smc/smc_core.c | 30 +++++++++++++++++++-----------
 1 file changed, 19 insertions(+), 11 deletions(-)

diff --git a/net/smc/smc_core.c b/net/smc/smc_core.c
index e2d083daeb7e..a18730edb7e0 100644
--- a/net/smc/smc_core.c
+++ b/net/smc/smc_core.c
@@ -2314,6 +2314,10 @@ int smcr_buf_reg_lgr(struct smc_link *lnk)
 	return rc;
 }
 
+/*
+ * smcr_new_buf_create may allocate a buffer smaller than the requested
+ * bufsize. Use buf_desc->len to determine the actual allocated size.
+ */
 static struct smc_buf_desc *smcr_new_buf_create(struct smc_link_group *lgr,
 						int bufsize)
 {
@@ -2326,18 +2330,22 @@ static struct smc_buf_desc *smcr_new_buf_create(struct smc_link_group *lgr,
 
 	switch (lgr->buf_type) {
 	case SMCR_PHYS_CONT_BUFS:
+		bufsize = min(bufsize, (int)PAGE_SIZE << MAX_PAGE_ORDER);
+		fallthrough;
 	case SMCR_MIXED_BUFS:
 		buf_desc->order = get_order(bufsize);
-		buf_desc->pages = alloc_pages(GFP_KERNEL | __GFP_NOWARN |
-					      __GFP_NOMEMALLOC | __GFP_COMP |
-					      __GFP_NORETRY | __GFP_ZERO,
-					      buf_desc->order);
-		if (buf_desc->pages) {
-			buf_desc->cpu_addr =
-				(void *)page_address(buf_desc->pages);
-			buf_desc->len = bufsize;
-			buf_desc->is_vm = false;
-			break;
+		if (buf_desc->order <= MAX_PAGE_ORDER) {
+			buf_desc->pages = alloc_pages(GFP_KERNEL | __GFP_NOWARN |
+						      __GFP_NOMEMALLOC | __GFP_COMP |
+						      __GFP_NORETRY | __GFP_ZERO,
+						      buf_desc->order);
+			if (buf_desc->pages) {
+				buf_desc->cpu_addr =
+					(void *)page_address(buf_desc->pages);
+				buf_desc->len = bufsize;
+				buf_desc->is_vm = false;
+				break;
+			}
 		}
 		if (lgr->buf_type == SMCR_PHYS_CONT_BUFS)
 			goto out;
@@ -2476,7 +2484,7 @@ static int __smc_buf_create(struct smc_sock *smc, bool is_smcd, bool is_rmb)
 		}
 
 		SMC_STAT_RMB_ALLOC(smc, is_smcd, is_rmb);
-		SMC_STAT_RMB_SIZE(smc, is_smcd, is_rmb, true, bufsize);
+		SMC_STAT_RMB_SIZE(smc, is_smcd, is_rmb, true, buf_desc->len);
 		buf_desc->used = 1;
 		down_write(lock);
 		smc_lgr_buf_list_add(lgr, is_rmb, buf_list, buf_desc);
-- 
2.45.0